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LibWeb: Avoid rebuilding layout tree unless CSS display property changes

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Before this, any style change that mutated a property we consider
"layout-affecting" would trigger a complete teardown and rebuild of the
layout tree.

This isn't actually necessary for the vast majority of CSS properties,
so this patch makes the invalidation a bit finer, and we now only
rebuild the layout tree when the CSS display property changes.

For other layout-affecting properties, we keep the old layout tree (if
we have one) and run the layout algorithms over that once again.
This is significantly faster, since we don't have to run all the CSS
selectors all over again.
This commit is contained in:
Andreas Kling 2023-05-22 16:09:15 +02:00
parent 8f5cc613d2
commit 821f808e52
3 changed files with 66 additions and 53 deletions
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75
Userland/Libraries/LibWeb/DOM/Element.cpp
View file

@ -395,52 +395,48 @@ void Element::did_remove_attribute(DeprecatedFlyString const& name)
}
}
enum class RequiredInvalidation {
None,
RepaintOnly,
RebuildStackingContextTree,
Relayout,
};
static RequiredInvalidation compute_required_invalidation(CSS::StyleProperties const& old_style, CSS::StyleProperties const& new_style)
static Element::RequiredInvalidationAfterStyleChange compute_required_invalidation(CSS::StyleProperties const& old_style, CSS::StyleProperties const& new_style)
{
Element::RequiredInvalidationAfterStyleChange invalidation;
if (&old_style.computed_font() != &new_style.computed_font())
return RequiredInvalidation::Relayout;
bool requires_repaint = false;
bool requires_stacking_context_tree_rebuild = false;
invalidation.relayout = true;
for (auto i = to_underlying(CSS::first_property_id); i <= to_underlying(CSS::last_property_id); ++i) {
auto property_id = static_cast<CSS::PropertyID>(i);
auto const& old_value = old_style.properties()[i];
auto const& new_value = new_style.properties()[i];
if (!old_value && !new_value)
continue;
if (!old_value || !new_value)
return RequiredInvalidation::Relayout;
if (*old_value == *new_value)
bool const property_value_changed = (!old_value || !new_value) || *old_value != *new_value;
if (!property_value_changed)
continue;
// NOTE: If the computed CSS display property changes, we have to rebuild the entire layout tree.
// In the future, we should figure out ways to rebuild a smaller part of the tree.
if (property_id == CSS::PropertyID::Display) {
return Element::RequiredInvalidationAfterStyleChange::full();
}
// OPTIMIZATION: Special handling for CSS `visibility`:
if (property_id == CSS::PropertyID::Visibility) {
// We don't need to relayout if the visibility changes from visible to hidden or vice versa. Only collapse requires relayout.
if ((old_value->to_identifier() == CSS::ValueID::Collapse) != (new_value->to_identifier() == CSS::ValueID::Collapse))
return RequiredInvalidation::Relayout;
if ((old_value && old_value->to_identifier() == CSS::ValueID::Collapse) != (new_value && new_value->to_identifier() == CSS::ValueID::Collapse))
invalidation.relayout = true;
// Of course, we still have to repaint on any visibility change.
requires_repaint = true;
invalidation.repaint = true;
} else if (CSS::property_affects_layout(property_id)) {
return RequiredInvalidation::Relayout;
invalidation.relayout = true;
}
if (CSS::property_affects_stacking_context(property_id))
requires_stacking_context_tree_rebuild = true;
requires_repaint = true;
invalidation.rebuild_stacking_context_tree = true;
invalidation.repaint = true;
}
if (requires_stacking_context_tree_rebuild)
return RequiredInvalidation::RebuildStackingContextTree;
if (requires_repaint)
return RequiredInvalidation::RepaintOnly;
return RequiredInvalidation::None;
return invalidation;
}
Element::NeedsRelayout Element::recompute_style()
Element::RequiredInvalidationAfterStyleChange Element::recompute_style()
{
set_needs_style_update(false);
VERIFY(parent());
@ -448,30 +444,25 @@ Element::NeedsRelayout Element::recompute_style()
// FIXME propagate errors
auto new_computed_css_values = MUST(document().style_computer().compute_style(*this));
auto required_invalidation = RequiredInvalidation::Relayout;
RequiredInvalidationAfterStyleChange invalidation;
if (m_computed_css_values)
required_invalidation = compute_required_invalidation(*m_computed_css_values, *new_computed_css_values);
invalidation = compute_required_invalidation(*m_computed_css_values, *new_computed_css_values);
else
invalidation = RequiredInvalidationAfterStyleChange::full();
if (required_invalidation == RequiredInvalidation::None)
return NeedsRelayout::No;
if (invalidation.is_none())
return invalidation;
m_computed_css_values = move(new_computed_css_values);
if (required_invalidation == RequiredInvalidation::RepaintOnly && layout_node()) {
if (!invalidation.rebuild_layout_tree && layout_node()) {
// If we're keeping the layout tree, we can just apply the new style to the existing layout tree.
layout_node()->apply_style(*m_computed_css_values);
layout_node()->set_needs_display();
return NeedsRelayout::No;
if (invalidation.repaint)
layout_node()->set_needs_display();
}
if (required_invalidation == RequiredInvalidation::RebuildStackingContextTree && layout_node()) {
layout_node()->apply_style(*m_computed_css_values);
document().invalidate_stacking_context_tree();
layout_node()->set_needs_display();
return NeedsRelayout::No;
}
return NeedsRelayout::Yes;
return invalidation;
}
NonnullRefPtr<CSS::StyleProperties> Element::resolved_css_values()